Method of roasting zinc sulphide ores



Oct. 10, 1933. A. L. J. QUENEAU 1,930,370

METHOD OF ROASTING ZINC SULIHIDE ORES Filed Oct. 25, 1929 4 Sheets-Sheet l avwemtoz Oct. 10, 1933. A. L. J. QUENEAU METHOD OF ROASTING ZINC SULPHIDE ORES 4 Sheets-Sheet 3 Filed Oct. 25. 1929 awuontop AUGUJ'Tl/VL EO/V Jew/v QUE/V54 Oct. 10, 1933. A. J. QUENEAU METHOD OF ROASTING ZINC SULPHIDE ORES Filed Oct. 25. 1929 4 Sheets-Sheet 4 sq W $1 6n Patented Oct. '10, 1933 UNITED STATES PATENT OFFICE Augustin Leon Jean Queneau, New York, N. Y.

Application October 25,

I 6 Claims.

This invention relates to an improved method and apparatus for the treatment of sulphide ores. While not limited thereto the invention is particularly well suited for the treatment of zinc bearing materials.

Heretofore in order to produce zinc, it has been necessary to have the zinc bearing material in the form of an oxide regardless of whether the material was to be reduced either by the old retort process or by the electrolytic method. The most abundant form of zinc ore unfortunately is in the form of zinc sulphide which so far as I am aware has never before been reduced to metal by any known method. In order to bring about reduction it has heretofore been necessary to roast the sulphide ore so as to transform it from the sulphide to the oxide form. The oxidation produces a strongly exothermic reaction. Zinc sulphide is a very dense material and the oxidation thereof takes place at an extremely slow rate and proceeds only on the exposed surface.

In the early days, zinc sulphide ore was usually roasted in hand fed fired furnaces of primitive construction. But owing to increasing cost of labor and the difliculty of securing skilled operators, different types of mechanical furnaces have more recently been introduced. However,

, insofar as Iam informed, none of the later furnaces are effective to produce an ore which is substantially free from sulphur at the end of the operation without the use of fuel. In other words, the conventional types of furnace are incapable of securing what is called in the art a dead roast. In all cases it has heretofore been necessary to burn a certain amount of fuel such as coal, oil, gas, etc., to complete the roasting of the ore. Aside from the increased cost of fuel, this is not detrimental if the prodnets of combustion are not to be used for the manufacture of sulphuric acid. If, however, sulphuric acid is to be made, it is necessary to have a concentrated sulphur dioxide gas free from carbon compounds. The necessity of separating the carbonaceous products of combustion from the sulphur compounds has led to the utilization of somewhat complicated furnace structures provided with so-called muffle hearths in.

which the heat is transmitted from the hot products of combustion of the carbonaceous fuel to the sulphide ore under treatment; such heat being transmitted through suitable refractory walls. The ineflficiency of this prior practice is thought to be self-evident.

In the usual roasting operation, the heat liber- 1929. Serial No. 402,418

ation is extremely rapid at the beginning of the roast where there is abundant sulphur and on the other hand is extremely slow toward the end of the roast where there is a deficiency of sulphur available. Thus, in the prior practice, there was an excessive heat liberation at the beginning and a deficiency at the end of the roast. It has heretofore been proposed to introduce green ore (unroasted ore) at different points in the furnace. In one known type of furnace (the McDougal shelf-roaster) and in subsequent modifications thereof, the ore to be roasted is caused to circulate progressively from shelves by means of a suitable mechanical device having a number of rabbling arms. In this former type of roaster means have been provided for feeding the green ore tothe lower hearths and the activity of oxidation has been increased and it has been almost possible to secure the so-called dead roast without the use of extraneous fuel. The operation may be said to be an autogenous roasting. In the well known type of furnace heretofore used, zinc ore has been roasted down to approximately 4% to l /2% of residual sulphur without the use of additional carbonaceous fuel.

One object of the present invention is to secure substantially the same result, but by a different and more efficient'method hereinafter described; moreover, the invention applies particularlyto the dead roasting of sulphide ores in such a manner that sulphuric acid can be recovered economically from the outgoing gas products. Another object of the invention is to provide improved apparatus whereby sulphur or brimstone can be burned without the sulphur coming into detrimental .contact with the ore bein treated. Y

The invention will be fully apparent from the following specification when read in connection with the accompanying drawings, wherein:

Fig. 1 is a longitudinal section through an apparatus embodyingcertain features of the invention;

Fig. 2 is a plan view of the apparatus;

Fig. 3 is an elevation of the roaster;

Fig. 4 is an enlarged detail on line 1-4 of Fig. 2;

Fig. 5 is a vertical section on line 5-5 of Fig. 4.

Referring in detail to the drawingsQlO represents a sulphur roasting furnace having a plurality' of superposed shelves 12 over which the ore fed' from the hopper 14 travels progressively from top to bottom, the same being propelled by air cooled rabbling arms 16 carried by a hollow central shaft 18 driven by suitable motor driven mechanism indicated at 20.

I provide a steel vessel indicated at 22 which has a steam coil 24 for maintaining in molten condition a body of sulphur, indicated at 26. This sulphur is adapted to be led throughsuitable steam jacketed pipes indicated at 28 to a. plurality of sulphur burners indicated at 30. Each pipe 28 will be provided with a valve 32 by means of which the quantity of liquid sulphur fed 'to the burner can be varied manually so as to secure a fine degree of adjustment.

Each burner 30 is enclosed in a chamber structure 34 secured to the outer shell of the roaster. As best shown in Figs. 4 and 5, each burner 30 includes a plurality of superposed pans 36, each having legs 38 on which they are supported in proper relationship. Each pan is provided with an apertured lug 40 forming an overflow port so as to maintain levels of sulphur at points indicated at 42 in Fig. 4. With this arrangement, it is impossible for the molten sulphur from the several pans 36 to overflow or to in any way come into detrimental contact with the ore being treated on the hearth of the roaster. The overflow 40 of the lowermost pan 36 empties into a catch basin 44 having an outlet 46, which in turn empties into a pipe 48 leading to any suitablevessel outside of the roaster.

For supporting combustion of the'molten sulphur supplied to the several pans 36 of the burners 30, I provide means for introducing heated air to the chamber members 34 which enclose the burner pans. l

- As best shown in Figs. 1 to 3 air is supplied under pressure by a suitable fan or blower 50 through a pipe 51 to the hollow shaft-18. This air serves to cool the shaft and the several rabbling arms 16, and a portion of this air passes through openings 19 into the furnace to support the oxidation of the ore upon the shelves 12. The air in passing through the shaft 18 and rabbling arms is preheated and a certain proportion thereof is passed through an air regulating valve 52 to a down-comer pipe 54. This pipe is provided with a flow meter 56 and a regu-' lating valve 58 by means of which the operator can accurately supply the requisite amount of air to take care of the combustion needs of the furnace and so as to maintain a proper proportion of air and sulphur. J

Branch pipes 56 lead from the lower portion of the pipe 54 to the several burners. Each branch} pipe is equipped with a regulating valve 58 and a gauge 60 by means of which the operator can accurately determine and maintain the pressure of airsupplied. t

A high grade zinc sulphide ore usually contains approximately 30% of sulphur; thus, by adding green ore as heretofore done in the zone where there is usually a deficiencypf heat, former operators add only 30% by weight'of the ore addition as the sulphur fuel.

According to my improved method instead of adding the sulphur fuel in the form of sulphide ore in a solid state, I add 100% sulphur fuel by weight. I am enabled to do this by introducing brimstone or pure sulphur and heated air.

Sulphur at ordinary temperatures is a solid. It usually occurs in lump form and it is rather difficult to obtain in a fine state of division such as would be required for close regulation of quantities such as would be accurately introduced at various points of a roasting furnace.

To overcome this difficulty according to my improved method, I melt the sulphur and introduce the resulting liquid through suitable steam jacketed pipes to different parts of the roasting furnace. The supply of liquid sulphur to any desired part of the roasting furnace is controlled by a simple stop-cock, as above described.

Sulphur melts at a low temperature (about l16.5 C.) and this temperature can readily be reached by the use of steam at approximately a pressure of 100 pounds at a temperature of 164 C. In dead roasting zinc ore it is necessary to raise the temperature on the last hearth to about 900 C. and above in order to break up the residual zinc sulphate which dissociates at 767 C. but in order to obtain complete and rapid dissociation in the ore bed a temperature of 900 C. is a necessity. To obtain this high temperature it has been necessary heretofore to use exclusively for dead roasting some form of carbonaceous fuel or hydrocarbon. If the roast gases are to be used for acid manufacture the amount of fuel used, outside of other economic considerations, is to be restricted and in any event the H20 and C02 contents of the ficiency of the acid plant. It is the usual practice to burn this type of fuel in so-called mufile chambers out of contact with the ore under treatment, the products of combustion being released to the atmosphere. The heat of combustion is conducted to ore under treatment by conduction through the refractory walls.

It is to avoid the use of carbonaceous or hydrocarbon fuels with the resulting disadvantages that I-use brimstone sulphur. However, to obtain a satisfactory utilization of its calorific power it is preferable to burn it under the specified conditions herein disclosed:

In the practice of the invention I admit preheated air at say 250 0., preferably higher. this air being taken conveniently from the air used to cool the shaft and rabble arms of the roasting furnace and I limit the amount of airso as to have almost perfect combustion with 15% or better S02 in the products of combustion leaving the sulphur burner. The temperature of combustion under this strictly controlled method of combustion is theoretically 1225 C. and making due allowance for all heat losses, the temperature level of practically 900 C. or 1000 C. is attained.

For good practice, I have determined that in order to secure a dead roast of zinc ore there is a consumption of from 10% to 12% of sulphur brimstone burned .as fuel for each ton of green ore treated. That is to say, for each ton of green ore I burn approximately 200 to 240 pounds of brimstone sulphur fuel.

In order to maintain the most eificient roasting conditions, preheated air is preferably supplied under pressure to the several sulphur burners in such carefully regulated quantities with relation to the amount of sulphur fuel supplied to the burners so as to maintain a temperature of not less than 900 C. on the lowest hearth. Under these conditions the products of combustion leaving the burner will include from 10% to 15% or more S02.

In Fig. l, I have indicated that the molten sulphur is fed by gravity to the uppermost pan of the burner and the rate of flow thereto is controlled accurately by a valve. The valve permits the operator to accurately control the amount of sulphur fed in accordance with the amount of air supplied to the burner so as to maintain .proper operating conditions. Instead of having a gravity feed for the sulphur, in practice sulphur will be preferably fed at an accurately determined rate by means of a gear pump and the supply of air to the burner will ,be regulated in accordance with the supply of fuel, it being understood from the foregoing that an important feature of the invention resides in accurately maintaining a predetermined proportion between the amount of fuel and the amount of air supplied to the furnace whereby an almost perfect combustion of sulphur is secured so that the products of combustion leaving the burner contain preferably not less than 10% S02.

The maintenance of these conditions enables me to hold the temperature in the lower part of the apparatus from between 900 to 1000 C.

The above described method is in part an improvement and continuation of the method described in my pending application No. 245,545, filed January 9, 1928.

While I have described quite specifically certain relative amounts of sulphurous fuel and certain preferred temperatures it is to be understood that such specific examples are to be interpreted in an illustrative rather than a lim-' iting sense.

What I claim is:

1. The method of dead roasting oxidized zinc sulphide ores which comprises circulating over said ores an air-sulphur dioxide gas admixture heated to temperatures in excess of the thermal decomposition temperature of metal sulphate compounds contained in said ores.

2. The method of dead roasting oxidized zinc sulphide ores which comprises heating said ores to temperatures in excess of the thermal decomposition temperature of metal sulphate compounds contained therein by circulating thereover an air-sulphur dioxide gas admixture heated to temperatures in excess of the said thermal decomposition temperature.

3. In the roasting ofzinc sulphide ores, the method of dead roasting the same which com- Patent No. l, 930, 370.

'over a hearth and circulating thereover an atmosphere comprised of air and sulphur dioxide heated to temperatures in excess of the thermal decomposition temperature of metal sulphate compounds contained in said ore.

4. In the roasting of zinc sulphide ores, the method of dead roasting the same which comprises oxidizing the ore in a furnace of the multiple hearth type, progressively feeding said ore from the top hearth to the bottom hearth of said furnace, and circulating over the bottom hearth of said furnace an air-sulphur dioxide gas admixture heated externally of said furnace to temperatures in excess of the thermal decomposition temperature of metal sulphates contained in saidore.

5. In the roasting of zinc ores in accordance with the method defined by claim 29, the method of heating the air-sulphur dioxide gas admixture for circulation over the lower hearths of said furnace which comprises melting substantially pure sulphur, feeding saidmolten sulphur to a sulphur burner, supplying to said burner air preheated to temperatures at least approximating 250 C. and controlling the quantity of said air to obtain substantially perfect combustion of said sulphur with said air and passing the gaseous products of combustion of said burner directly into said furnace at a point adjacent the lower hearths thereof without permitting appreciable loss of the sensible heat of said gases.

6. In the roasting of zinc ores in accordance with the method defined by claim 29, the method of heating the air-sulphur dioxide gas admixture for circulation over the lower hearths of said furnace which comprises melting substantially pure sulphur, feeding said molten sulphur to a sulphur burner, supplying 'to said burner air preheated to temperatures at least approximating 250 C. and controlling the quantity of said air to obtain a gaseous product of combustion containing at least approximately. 15 per cent sulphur dioxide and passing the gaseous products of combustion of said burner directly into said furnace at a point adjacent the lower'hearths thereof without permitting appreciable loss of thesensible heat of said gases.

AUGUSTIN LEON JEAN QUENEAU.

CERTIFICATE OF CORRECTION.

October 10, 1933.

It is hereby certified that error appears in the printed specification ofthe above numbered patent requiringcorrection as follows: Page 3,- lines 94 and 109, claimsS and 6, respectively.- for "29" read4; and that the said Letters Patent should beread with these corrections therein that the same may conform to the A record of the case in the Patent Office.

Signed and sealed this 28th day of (Seal) November, A. I). 1933.

F. M. Hopkins .Acting Commissioner of Patents. 

